Table 2.

Abridged adjustment factors.

AAltitude, exposure (Table 3) and climatic conditions
1.aHigh-altitude (>300 m) localities (add 4 for >400 m)Up to 4
1.bHigh-altitude localities or coastal locations that are also slightly, moderately or very exposed2 to 7
1.cModerately or very exposed, moderate-altitude (150–300 m) localities1 to 4
1.dModerately or very exposed, low-altitude (<150 m) localities1 to 3
2.aFrost or moisture pockets and sites of cold air drainage1 to 4
2.bSun trapsUp to 3
BAspect
1.aNortherly or westerly aspect12 to 4
1.bEasterly to southerly aspects10 or 1
CGroundwater and surface runoff
1.aRock surface dry, no evidence of seepage or very localized surface dampness20 to 1
1.bLocalized slow dripping or moderate areas of damp or wet rock21 to 2
1.cSteady dripping, light continuous flow or large areas of wet rock surface21 to 4
1.dModerate, continuous flow23 to 7
1.eExcessive, continuous, strong flow24 to 9
DStatic stress
1Deep excavations (e.g. where overburden depth removed >20 m) in strong, massive rock. This adjustment should be ignored for EXISTING rockslopes. Apply the maximum adjustment for very deep excavations (>50 m)Up to 3
2Surcharge at the slope crest (e.g. structures, trees). Refer to H3cUp to 2
EDynamic stress
1.aDynamic loading owing to quarry blasting in close proximity (<100 m) to the slope1 to 3
1.bGround vibration owing to traffic movement on high-speed roads in very close proximity (<10 m) to the slope2 to 4
FExcavation method
Excavation method adjustments should be ignored for EXISTING rockslopes. For PROPOSED rockslopes, obtain an adjustment from the ‘RDA Rating adjustment for excavation methods’ (Fig. 3)
GStabilization and protective measures
1Deterioration associated with EXISTING stabilization measures (e.g. material weathering around rockbolt heads; spalling associated with drainholes, rockbolts and dowels). Apply a low adjustment unless a widespread effectUp to 3
HVegetation cover
Highly weathered or soil-like slopes (excluding highly fractured rockslopes)
1.aCover of grass or other fine-rooted, low-growing, herbaceous plants−10 to −2
1.bSmall woody shrubs and trees (up to 3 m height)−6 to 0
1.cWidespread, dense cover of large woody shrubs and trees (exceeding 3 m height)−4 to −2
2Isolated growth of large woody shrubs and trees (exceeding 3 m height)0 to 2
Slopes cut in rock (including highly fractured rockslopes)
3.aCover of grass or other fine-rooted, low-growing herbaceous plants0 to 3
3.bSmall woody shrubs and trees (up to 3 m height)1 to 5
3.cLarge woody shrubs and trees (exceeding 3 m height)2 to 7
JSlope geometry
1.aSlopes (or individual risers in benched excavations) with a height >15 m2 to 5
1.bSlopes wholly or partly composed of benches less than 1.5 m in height−2 to −5
1.cSlopes with a total height less than 4 m−2 to −3
2.aUniform, planar surface with little irregularity or large-scale roughness in highly weathered or soil-like materials. Apply only to EXISTING slopesUp to 3
2.bUniform, planar surface with little irregularity or large-scale roughness on slopes cut in rock. Apply only to EXISTING slopes−3 to 0
KRock mass structure
For rock masses with extremely poor material properties and vice versa and where the RDAU Rating for the two unfavourable parameters is >35, the total RDAU Rating must be adjusted as in 1 below using the chart given in Fig. 4
1.aWhere RDAU for the two favourable parameters is 0–10% of the rating for the two unfavourable parameters13
1.bWhere RDAU for the two favourable parameters is 10–20% of the rating for the two unfavourable parameters9
1.cWhere RDAU for the two favourable parameters is 20–30% of the rating for the two unfavourable parameters5
2.aA single, dominant, regular set of regular fractures such that there are very few discontinuity intersections−1 to −7
2.bRock mass dominated by angular, blocky shapes with at least one acute angle (e.g. highly interlocking)−3 to 0
3Highly variable or composite rock mass containing discrete zones of contrasting rock mass and/or material properties (e.g. highly fractured areas, shear zones), which cannot be evaluated separately0 to 7 or −7 to 0
4Favourability of dip angle and direction for recurring fracture sets (favourable = 0; unfavourable = 1–3; very unfavourable = 3–6)Up to 6
LTime since excavation
1.aAll natural slopes, and slopes excavated more than 80 years ago−10 to −8
1.bSlopes excavated between 50 and 80 years ago−8 to −5
1.cSlopes excavated between 30–50 years ago−4 to −1
1.dPre-split blasted or slopes excavated mechanically 5–30 years ago−5 to −2
1.ePre-split blasted or slopes excavated mechanically in the last 5 years−2 to 0
MDirect disturbance
1Anthropogenic disturbance (e.g. walking, climbing, grazing, fossil collecting)1 to 3
2Basal undercutting (e.g. marine action; river erosion; weathering, collapse or erosion of underlying rock)1 to 6
  • 1An aspect adjustment should not be applied for sheltered slopes, or for slopes where either adjustment A2a or A2b has been applied.

  • 2Apply a lower adjustment where flow is very localized and a higher value if widespread. Apply the adjustment for the worst case.